I am chasing what I think might be an indication issue on a King Air E-90. It has been modified with a 5-Bladed propeller. Usually I would use a digital prop tach but they only have a 2 or three bladed setting.

I don't know exactly what the prop RPM on the Kingair is, but I'll betcha it's somewhere between 2000 and 2500. Easily read with a heli tach.

There, their and they're. It's really that simple.

Try a model airplane tach with a tube on it's optics aimed at the prop arc. As mentioned earlier for your 5 bladed prop, set for 2 blades and divide the reading by 2.5 (times 2 then divide by 5) or easier yet (times 4 then divide by 10)